------------------------------
 
 Date:� � Sat, 21 Dec 2013 20:56:20 -0800
 From:� � Stuart <ve3smf@YAHOO.COM>
 Subject: Re: Van Dies while in motion
 
 Ref:=C2=A0 http://ecmweb.com/design/highs-and-lows-motor-voltage=0A=C2=A0=
 =0A"To drive a fixed mechanical load connected to the shaft,
 a motor must d=
 raw a fixed amount of power from the line. The amount of
 power the motor dr=
 aws has a rough correlation to the voltage 2current (amps).
 Thus, when volt=
 age gets low, the current must increase to provide the same
 amount of power=
 . "=0A=C2=A0=0A"The Highs and Lows of Motor Voltage=0AMay 1,
 2000 12:00 PM,=
  By Ed Cowern, P.E.=0AOperating a motor at the "outer
 limits" of its voltag=
 e requirements reduces its efficiency and causes premature
 failure.=0AThe e=
 conomic loss from premature motor failure is devastating. In
 most cases, th=
 e price of the motor itself is trivial compared to the cost
 of unscheduled =
 shutdowns of processes. Both high and low voltages can cause
 premature moto=
 r failure, as will voltage imbalance. Here, we'll look at
 the effects of lo=
 w and high voltage on motors and the related performance
 changes you can ex=
 pect when you use voltages other than those noted on the
 nameplate.=0AEffec=
 ts of low voltage. When you subject a motor to voltages
 below the nameplate=
  rating, some of the motor's characteristics will change
 slightly and other=
 s will change dramatically. To drive a fixed mechanical load
 connected to t=
 he shaft, a motor must draw a fixed amount of power from the
 line. The amou=
 nt of power the motor draws has a rough correlation to the
 voltage 2current=
  (amps). Thus, when voltage gets low, the current must
 increase to provide =
 the same amount of power. An increase in current is a danger
 to the motor o=
 nly if that current exceeds the motor's nameplate current
 rating. When amps=
  go above the nameplate rating, heat begins to build up in
 the motor. Witho=
 ut a timely correction, this heat will damage the motor. The
 more heat and =
 the longer the exposure to it, the more damage to the
 motor."=0A=0AAnother =
 source from the same author...=0A=0ARef:=C2=A0 http://www.motorsanddrives.c=
 om/cowern/motorterms12.html=0A=0A" =0ALOW VOLTAGE=0AWhen
 electric motors ar=
 e subjected to voltages, below the nameplate rating, some of
 the characteri=
 stics will change slightly and others will change more
 dramatically. A basi=
 c point is, to drive a fixed mechanical load connected to
 the shaft, a moto=
 r must draw a fixed amount of power from the power line. The
 amount of powe=
 r the motor draws is roughly related to the voltage times
 current (amps). T=
 hus, when voltage gets low, the current must get higher to
 provide the same=
  amount of power. The fact that current gets higher is not
 alarming unless =
 it exceeds the nameplate current rating of the motor. When
 amps go above th=
 e nameplate rating, it is safe to assume that the buildup of
 heat within th=
 e motor will become damaging if it is left unchecked. If a
 motor is lightly=
  loaded and the voltage drops, the current will increase in
 roughly the sam=
 e proportion that the voltage decreases.=0AFor example, a
 10% voltage decre=
 ase would cause a 10% amperage increase. This would not be
 damaging if the =
 motor current stays below the nameplate value. However, if a
 motor is heavi=
 ly loaded and a voltage reduction occurs, the current would
 go up from a fa=
 irly high value to a new value which might be in excess of
 the full load ra=
 ted amps. This could be damaging. It can be safely said that
 low voltage in=
  itself is not a problem unless the motor amperage is pushed
 beyond the nam=
 eplate rating.=0A=C2=A0=0AAside from the possibility of
 over-temperature an=
 d shortened life created by low voltage, some other
 important items need to=
  be understood. The first is that the starting torque,
 pull-up torque, and =
 pull-out torque of induction motors, all change based on the
 applied voltag=
 e squared . Thus, a 10% reduction from nameplate voltage
 (100% to 90%, 230 =
 volts to 207 volts) would reduce the starting torque,
 pull-up torque, and p=
 ull-out torque by a factor of .9 x .9. The resulting values
 would be 81% of=
  the full voltage values. At 80% voltage, the result would
 be .8 x .8, or a=
  value of 64% of the full voltage value.=0A=C2=A0=0AIn this
 case, it is eas=
 y to see why it would be difficult to start
 =E2=80=9Chard-to-start=E2=80=9D=
  loads if the voltage happens to be low. Similarly the
 motor=E2=80=99s pull=
 -out torque would be much lower than it would be under
 normal voltage condi=
 tions.=0A=C2=A0=0ATo summarize the situation, low voltage
 can cause high cu=
 rrents and overheating which will subsequently shorten motor
 life. Low volt=
 age can also reduce the motor=E2=80=99s ability to get
 started and its valu=
 es of pull-up and pull-out torque. On lightly loaded motors
 with easy-to-st=
 art loads, reducing the voltage will not have any
 appreciable effect except=
  that it might help reduce the light load losses and improve
 the efficiency=
  under this condition. This is the principle that is used in
 the so-called =
 Nola devices that are sold as efficiency improving add-on
 equipment to moto=
 rs."=C2=A0=0ALook at the digram in the article.=C2=A0 You
 can see with a re=
 duction in voltage, you get a corresponding increase in
 current.=C2=A0 In t=
 he given case, I suspect that the battery and/or the
 alternator failed, wit=
 h a resulting=C2=A0 voltage drop.=C2=A0 With several high
 power devices, su=
 ch as fans and lights, the current demands on the wiring
 would have gone up=
 .=C2=A0 Perhaps this caused overheating of the switch and
 system failure.=
 =C2=A0 This will only be answered when the original poster
 tells what devic=
 es failed.=C2=A0 State of the battery, alternator, switch
 and other wirng.=
 =0A=0AWhat do you think happened?=C2=A0 Your
 thoughts......=0A=0ACheers!=0A=
 Stuart=0A=0A________________________________=0AFrom: Larry
 Alofs <lalofs@gm=
 ail.com>=0ATo: Stuart <ve3smf@yahoo.com>
 =0ACc: vanagonlist a <vanagon@gerr=
 y.vanagon.com> =0ASent: Saturday, December 21, 2013
 10:33:59 PM=0ASubject: =
 Re: Van Dies while in motion=0A=0A=0A=0AStuart, =0A=C2=A0
 I'm afraid you ar=
 e too far out on your limb. =C2=A0Your basic starting point
 that any device=
  will use a fixed amount of power is incorrect.=0AThat makes
 the rest of yo=
 ur argument and conclusions false.=0A=C2=A0 I am wondering
 where you came u=
 p with that premise.=0A=0ALarry A.

Stuart, you are citing information for *A/C* motors.  DC motors, and other resistive loads do not have power factors, and operate under simple Ohm's Laws.  A DC motor has a fixed (abeit temperature variant to a degree) internal resistance, and when voltage drops, it will respond according to the relationship E=IR.  R is fixed, thus when E drops, I drops as well.  Power dissipation (Volt-Amps, i.e. E*I) decreases as voltage decreases. If DC power were invariant as you claim, then a headlamp bulb would glow with the same luminosity at 1 VDC as at 14VDC.

Keith Hughes
'86 Westy Tiico (Marvin)